Miniature optical fiber pressure sensing systems have been used for a variety of applications. For example, the measurement of intravascular blood pressure of human patients has been accomplished using equipment manufactured by the present Assignee, FiberOptic Sensor Technologies, Inc. (FST), in which a diaphragm at the fiber sensing tip deforms in response to a pressure differential, thus modulating through reflection the light signal sent through the fiber. Changes in the distance between the deformed diaphragm and the optical fiber end, as well as the diaphragm shape, modulate the amplitude of light that is reflected back into the optical fiber. Accordingly, the intensity of the returned light signal is related to the pressure acting on the sensing tip.
Applicant has made numerous advancements in the technology of fiberoptic sensing systems which are principally oriented toward pressure measurement. The present Assignee, FST, also owns U.S. Pat. Nos. 4,701,246; 4,787,396; 4,856,317; 4,924,870; 5,247,171; 5,275,053; and 5,280,786, and co-pending U.S. applications with Ser. Nos. 08/132,718, filed on Oct. 6, 1993; 08/121,182, filed on Sep. 14, 1993; 08/128,849, filed on Sep. 29, 1993; and 08/109,361, filed on Aug. 19, 1993 which are related to various improvements in fiberoptic sensors and which are hereby incorporated by reference.
Furthermore, Applicant has made additional advancements in the technology of fiberoptic sensors for internal engine combustion chamber pressure measurement. These advancements are encompassed by Applicant's co-pending U.S. applications Ser. No. 08/087,631, and 08/086,245.
Particularly in health care applications, small size in-vivo pressure sensing catheters provide an accurate diagnostic tool when used in cardiology, urology, and trauma care, especially where invasive measurements and electrical bio-potential safety concerns necessitate use of small sensors and require electrical passiveness. Presently, use of the aforementioned intensity-based sensors utilize an optical fiber in front of a pressure sensing diaphragm which measures optical reflection to determine diaphragm displacement. These devices have proven to be practical, stable, small in size, and low in cost. However, one major limitation with use of these small-size diaphragm-type sensors is caused by their reduced sensitivity, i.e., a small diaphragm produces small deflections such that differential deflection must be more accurately quantified in order to obtain accuracy equivalent to that from a larger diaphragm sensor. Further design constraints increase the difficulty of providing such sensors having a desired frequency response range, long-term fatigue life, over-pressure protection, mechanical and optical stability and providing a structurally stable diaphragm when operating under a wide range of environmental conditions, including humidity and corrosion exposure. These requirements also restrict selection of a diaphragm's material, size, thickness, and strength parameters which reduce the ability to obtain an appropriate deflection range and sensitivity. In order to obtain improved sensor performance under the aforementioned mechanical constraints, techniques are needed to increase optical measurement sensitivity while still utilizing a small diaphragm sensor which compensates for the low mechanical responses of the diaphragm and improves overall performance over a broad range of applications.